diff --git a/lib/std/array_list.zig b/lib/std/array_list.zig
index 523d1c810f..c6bb5bf3e7 100644
--- a/lib/std/array_list.zig
+++ b/lib/std/array_list.zig
@@ -20,11 +20,9 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
     return struct {
         const Self = @This();
 
-        /// Use `span` instead of slicing this directly, because if you don't
-        /// specify the end position of the slice, this will potentially give
-        /// you uninitialized memory.
+        /// Content of the ArrayList
         items: Slice,
-        len: usize,
+        capacity: usize,
         allocator: *Allocator,
 
         pub const Slice = if (alignment) |a| ([]align(a) T) else []T;
@@ -34,7 +32,7 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         pub fn init(allocator: *Allocator) Self {
             return Self{
                 .items = &[_]T{},
-                .len = 0,
+                .capacity = 0,
                 .allocator = allocator,
             };
         }
@@ -49,60 +47,55 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
 
         /// Release all allocated memory.
         pub fn deinit(self: Self) void {
-            self.allocator.free(self.items);
+            self.allocator.free(self.allocatedSlice());
         }
 
+        /// Deprecated: use `items` field directly.
         /// Return contents as a slice. Only valid while the list
         /// doesn't change size.
-        pub fn span(self: var) @TypeOf(self.items[0..self.len]) {
-            return self.items[0..self.len];
+        pub fn span(self: var) @TypeOf(self.items) {
+            return self.items;
         }
 
-        /// Deprecated: use `span`.
+        /// Deprecated: use `items` field directly.
         pub fn toSlice(self: Self) Slice {
-            return self.span();
+            return self.items;
         }
 
-        /// Deprecated: use `span`.
+        /// Deprecated: use `items` field directly.
         pub fn toSliceConst(self: Self) SliceConst {
-            return self.span();
+            return self.items;
         }
 
-        /// Deprecated: use `span()[i]`.
+        /// Deprecated: use `list.items[i]`.
         pub fn at(self: Self, i: usize) T {
-            return self.span()[i];
+            return self.items[i];
         }
 
-        /// Deprecated: use `&span()[i]`.
+        /// Deprecated: use `&list.items[i]`.
         pub fn ptrAt(self: Self, i: usize) *T {
-            return &self.span()[i];
+            return &self.items[i];
         }
 
-        /// Deprecated: use `if (i >= list.len) return error.OutOfBounds else span()[i] = item`.
+        /// Deprecated: use `if (i >= list.items.len) return error.OutOfBounds else list.items[i] = item`.
         pub fn setOrError(self: Self, i: usize, item: T) !void {
-            if (i >= self.len) return error.OutOfBounds;
+            if (i >= self.items.len) return error.OutOfBounds;
             self.items[i] = item;
         }
 
-        /// Deprecated: use `list.span()[i] = item`.
+        /// Deprecated: use `list.items[i] = item`.
         pub fn set(self: *Self, i: usize, item: T) void {
-            assert(i < self.len);
+            assert(i < self.items.len);
             self.items[i] = item;
         }
 
-        /// Return the maximum number of items the list can hold
-        /// without allocating more memory.
-        pub fn capacity(self: Self) usize {
-            return self.items.len;
-        }
-
         /// ArrayList takes ownership of the passed in slice. The slice must have been
         /// allocated with `allocator`.
         /// Deinitialize with `deinit` or use `toOwnedSlice`.
         pub fn fromOwnedSlice(allocator: *Allocator, slice: Slice) Self {
             return Self{
                 .items = slice,
-                .len = slice.len,
+                .capacity = slice.len,
                 .allocator = allocator,
             };
         }
@@ -110,7 +103,7 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         /// The caller owns the returned memory. ArrayList becomes empty.
         pub fn toOwnedSlice(self: *Self) Slice {
             const allocator = self.allocator;
-            const result = allocator.shrink(self.items, self.len);
+            const result = allocator.shrink(self.allocatedSlice(), self.items.len);
             self.* = init(allocator);
             return result;
         }
@@ -118,10 +111,10 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         /// Insert `item` at index `n`. Moves `list[n .. list.len]`
         /// to make room.
         pub fn insert(self: *Self, n: usize, item: T) !void {
-            try self.ensureCapacity(self.len + 1);
-            self.len += 1;
+            try self.ensureCapacity(self.items.len + 1);
+            self.items.len += 1;
 
-            mem.copyBackwards(T, self.items[n + 1 .. self.len], self.items[n .. self.len - 1]);
+            mem.copyBackwards(T, self.items[n + 1 .. self.items.len], self.items[n .. self.items.len - 1]);
             self.items[n] = item;
         }
 
@@ -129,10 +122,10 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         /// `list[i .. list.len]` to make room.
         /// This operation is O(N).
         pub fn insertSlice(self: *Self, i: usize, items: SliceConst) !void {
-            try self.ensureCapacity(self.len + items.len);
-            self.len += items.len;
+            try self.ensureCapacity(self.items.len + items.len);
+            self.items.len += items.len;
 
-            mem.copyBackwards(T, self.items[i + items.len .. self.len], self.items[i .. self.len - items.len]);
+            mem.copyBackwards(T, self.items[i + items.len .. self.items.len], self.items[i .. self.items.len - items.len]);
             mem.copy(T, self.items[i .. i + items.len], items);
         }
 
@@ -153,13 +146,13 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         /// Asserts the array has at least one item.
         /// This operation is O(N).
         pub fn orderedRemove(self: *Self, i: usize) T {
-            const newlen = self.len - 1;
+            const newlen = self.items.len - 1;
             if (newlen == i) return self.pop();
 
-            const old_item = self.at(i);
+            const old_item = self.items[i];
             for (self.items[i..newlen]) |*b, j| b.* = self.items[i + 1 + j];
             self.items[newlen] = undefined;
-            self.len = newlen;
+            self.items.len = newlen;
             return old_item;
         }
 
@@ -167,26 +160,28 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         /// The empty slot is filled from the end of the list.
         /// This operation is O(1).
         pub fn swapRemove(self: *Self, i: usize) T {
-            if (self.len - 1 == i) return self.pop();
+            if (self.items.len - 1 == i) return self.pop();
 
-            const slice = self.span();
-            const old_item = slice[i];
-            slice[i] = self.pop();
+            const old_item = self.items[i];
+            self.items[i] = self.pop();
             return old_item;
         }
 
-        /// Deprecated: use `if (i >= list.len) return error.OutOfBounds else list.swapRemove(i)`.
+        /// Deprecated: use `if (i >= list.items.len) return error.OutOfBounds else list.swapRemove(i)`.
         pub fn swapRemoveOrError(self: *Self, i: usize) !T {
-            if (i >= self.len) return error.OutOfBounds;
+            if (i >= self.items.len) return error.OutOfBounds;
             return self.swapRemove(i);
         }
 
         /// Append the slice of items to the list. Allocates more
         /// memory as necessary.
         pub fn appendSlice(self: *Self, items: SliceConst) !void {
-            try self.ensureCapacity(self.len + items.len);
-            mem.copy(T, self.items[self.len..], items);
-            self.len += items.len;
+            const oldlen = self.items.len;
+            const newlen = self.items.len + items.len;
+
+            try self.ensureCapacity(newlen);
+            self.items.len = newlen;
+            mem.copy(T, self.items[oldlen..], items);
         }
 
         /// Same as `append` except it returns the number of bytes written, which is always the same
@@ -206,50 +201,58 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         /// Append a value to the list `n` times.
         /// Allocates more memory as necessary.
         pub fn appendNTimes(self: *Self, value: T, n: usize) !void {
-            const old_len = self.len;
-            try self.resize(self.len + n);
-            mem.set(T, self.items[old_len..self.len], value);
+            const old_len = self.items.len;
+            try self.resize(self.items.len + n);
+            mem.set(T, self.items[old_len..self.items.len], value);
         }
 
         /// Adjust the list's length to `new_len`.
         /// Does not initialize added items if any.
         pub fn resize(self: *Self, new_len: usize) !void {
             try self.ensureCapacity(new_len);
-            self.len = new_len;
+            self.items.len = new_len;
         }
 
         /// Reduce allocated capacity to `new_len`.
         /// Invalidates element pointers.
         pub fn shrink(self: *Self, new_len: usize) void {
-            assert(new_len <= self.len);
-            self.len = new_len;
-            self.items = self.allocator.realloc(self.items, new_len) catch |e| switch (e) {
-                error.OutOfMemory => return, // no problem, capacity is still correct then.
+            assert(new_len <= self.items.len);
+
+            self.items = self.allocator.realloc(self.allocatedSlice(), new_len) catch |e| switch (e) {
+                error.OutOfMemory => { // no problem, capacity is still correct then.
+                    self.items.len = new_len;
+                    return;
+                },
             };
+            self.capacity = new_len;
         }
 
         pub fn ensureCapacity(self: *Self, new_capacity: usize) !void {
-            var better_capacity = self.capacity();
+            var better_capacity = self.capacity;
             if (better_capacity >= new_capacity) return;
+
             while (true) {
                 better_capacity += better_capacity / 2 + 8;
                 if (better_capacity >= new_capacity) break;
             }
-            self.items = try self.allocator.realloc(self.items, better_capacity);
+            
+            const new_memory = try self.allocator.realloc(self.allocatedSlice(), better_capacity);
+            self.items.ptr = new_memory.ptr;
+            self.capacity = new_memory.len;
         }
 
         /// Increases the array's length to match the full capacity that is already allocated.
         /// The new elements have `undefined` values. This operation does not invalidate any
         /// element pointers.
         pub fn expandToCapacity(self: *Self) void {
-            self.len = self.items.len;
+            self.items.len = self.capacity;
         }
 
         /// Increase length by 1, returning pointer to the new item.
         /// The returned pointer becomes invalid when the list is resized.
         pub fn addOne(self: *Self) !*T {
-            const new_length = self.len + 1;
-            try self.ensureCapacity(new_length);
+            const newlen = self.items.len + 1;
+            try self.ensureCapacity(newlen);
             return self.addOneAssumeCapacity();
         }
 
@@ -257,25 +260,32 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         /// Asserts that there is already space for the new item without allocating more.
         /// The returned pointer becomes invalid when the list is resized.
         pub fn addOneAssumeCapacity(self: *Self) *T {
-            assert(self.len < self.capacity());
-            const result = &self.items[self.len];
-            self.len += 1;
-            return result;
+            assert(self.items.len < self.capacity);
+
+            self.items.len += 1;
+            return &self.items[self.items.len - 1];
         }
 
         /// Remove and return the last element from the list.
         /// Asserts the list has at least one item.
         pub fn pop(self: *Self) T {
-            self.len -= 1;
-            return self.items[self.len];
+            const val = self.items[self.items.len - 1];
+            self.items.len -= 1;
+            return val;
         }
 
         /// Remove and return the last element from the list.
         /// If the list is empty, returns `null`.
         pub fn popOrNull(self: *Self) ?T {
-            if (self.len == 0) return null;
+            if (self.items.len == 0) return null;
             return self.pop();
         }
+        
+        // For a nicer API, `items.len` is the length, not the capacity.
+        // This requires "unsafe" slicing.
+        fn allocatedSlice(self: Self) Slice {
+            return self.items.ptr[0..self.capacity];
+        }
     };
 }
 
@@ -283,15 +293,15 @@ test "std.ArrayList.init" {
     var list = ArrayList(i32).init(testing.allocator);
     defer list.deinit();
 
-    testing.expect(list.len == 0);
-    testing.expect(list.capacity() == 0);
+    testing.expect(list.items.len == 0);
+    testing.expect(list.capacity == 0);
 }
 
 test "std.ArrayList.initCapacity" {
     var list = try ArrayList(i8).initCapacity(testing.allocator, 200);
     defer list.deinit();
-    testing.expect(list.len == 0);
-    testing.expect(list.capacity() >= 200);
+    testing.expect(list.items.len == 0);
+    testing.expect(list.capacity >= 200);
 }
 
 test "std.ArrayList.basic" {
@@ -315,7 +325,7 @@ test "std.ArrayList.basic" {
         }
     }
 
-    for (list.span()) |v, i| {
+    for (list.items) |v, i| {
         testing.expect(v == @intCast(i32, i + 1));
     }
 
@@ -324,19 +334,19 @@ test "std.ArrayList.basic" {
     }
 
     testing.expect(list.pop() == 10);
-    testing.expect(list.len == 9);
+    testing.expect(list.items.len == 9);
 
     list.appendSlice(&[_]i32{ 1, 2, 3 }) catch unreachable;
-    testing.expect(list.len == 12);
+    testing.expect(list.items.len == 12);
     testing.expect(list.pop() == 3);
     testing.expect(list.pop() == 2);
     testing.expect(list.pop() == 1);
-    testing.expect(list.len == 9);
+    testing.expect(list.items.len == 9);
 
     list.appendSlice(&[_]i32{}) catch unreachable;
-    testing.expect(list.len == 9);
+    testing.expect(list.items.len == 9);
 
-    // can only set on indices < self.len
+    // can only set on indices < self.items.len
     list.set(7, 33);
     list.set(8, 42);
 
@@ -352,8 +362,8 @@ test "std.ArrayList.appendNTimes" {
     defer list.deinit();
 
     try list.appendNTimes(2, 10);
-    testing.expectEqual(@as(usize, 10), list.len);
-    for (list.span()) |element| {
+    testing.expectEqual(@as(usize, 10), list.items.len);
+    for (list.items) |element| {
         testing.expectEqual(@as(i32, 2), element);
     }
 }
@@ -378,17 +388,17 @@ test "std.ArrayList.orderedRemove" {
 
     //remove from middle
     testing.expectEqual(@as(i32, 4), list.orderedRemove(3));
-    testing.expectEqual(@as(i32, 5), list.at(3));
-    testing.expectEqual(@as(usize, 6), list.len);
+    testing.expectEqual(@as(i32, 5), list.items[3]);
+    testing.expectEqual(@as(usize, 6), list.items.len);
 
     //remove from end
     testing.expectEqual(@as(i32, 7), list.orderedRemove(5));
-    testing.expectEqual(@as(usize, 5), list.len);
+    testing.expectEqual(@as(usize, 5), list.items.len);
 
     //remove from front
     testing.expectEqual(@as(i32, 1), list.orderedRemove(0));
-    testing.expectEqual(@as(i32, 2), list.at(0));
-    testing.expectEqual(@as(usize, 4), list.len);
+    testing.expectEqual(@as(i32, 2), list.items[0]);
+    testing.expectEqual(@as(usize, 4), list.items.len);
 }
 
 test "std.ArrayList.swapRemove" {
@@ -405,17 +415,17 @@ test "std.ArrayList.swapRemove" {
 
     //remove from middle
     testing.expect(list.swapRemove(3) == 4);
-    testing.expect(list.at(3) == 7);
-    testing.expect(list.len == 6);
+    testing.expect(list.items[3] == 7);
+    testing.expect(list.items.len == 6);
 
     //remove from end
     testing.expect(list.swapRemove(5) == 6);
-    testing.expect(list.len == 5);
+    testing.expect(list.items.len == 5);
 
     //remove from front
     testing.expect(list.swapRemove(0) == 1);
-    testing.expect(list.at(0) == 5);
-    testing.expect(list.len == 4);
+    testing.expect(list.items[0] == 5);
+    testing.expect(list.items.len == 4);
 }
 
 test "std.ArrayList.swapRemoveOrError" {
@@ -478,7 +488,7 @@ test "std.ArrayList.insertSlice" {
 
     const items = [_]i32{1};
     try list.insertSlice(0, items[0..0]);
-    testing.expect(list.len == 6);
+    testing.expect(list.items.len == 6);
     testing.expect(list.items[0] == 1);
 }
 
@@ -504,3 +514,18 @@ test "std.ArrayList(u8) implements outStream" {
 
     testing.expectEqualSlices(u8, "x: 42\ny: 1234\n", buffer.span());
 }
+
+test "std.ArrayList.shrink still sets length on error.OutOfMemory" {
+        // use an arena allocator to make sure realloc returns error.OutOfMemory
+        var arena = std.heap.ArenaAllocator.init(testing.allocator);
+        defer arena.deinit();
+
+        var list = ArrayList(i32).init(&arena.allocator);
+
+        try list.append(1);
+        try list.append(2);
+        try list.append(3);
+
+        list.shrink(1);
+        testing.expect(list.items.len == 1);
+}
diff --git a/lib/std/array_list_sentineled.zig b/lib/std/array_list_sentineled.zig
index ee262b0322..b83cc4ad62 100644
--- a/lib/std/array_list_sentineled.zig
+++ b/lib/std/array_list_sentineled.zig
@@ -82,8 +82,8 @@ pub fn ArrayListSentineled(comptime T: type, comptime sentinel: T) type {
             self.list.deinit();
         }
 
-        pub fn span(self: var) @TypeOf(self.list.items[0 .. self.list.len - 1 :sentinel]) {
-            return self.list.span()[0..self.len() :sentinel];
+        pub fn span(self: var) @TypeOf(self.list.items[0..:sentinel]) {
+            return self.list.items[0..self.len() :sentinel];
         }
 
         pub fn shrink(self: *Self, new_len: usize) void {
@@ -98,16 +98,16 @@ pub fn ArrayListSentineled(comptime T: type, comptime sentinel: T) type {
         }
 
         pub fn isNull(self: Self) bool {
-            return self.list.len == 0;
+            return self.list.items.len == 0;
         }
 
         pub fn len(self: Self) usize {
-            return self.list.len - 1;
+            return self.list.items.len - 1;
         }
 
         pub fn capacity(self: Self) usize {
-            return if (self.list.items.len > 0)
-                self.list.items.len - 1
+            return if (self.list.capacity > 0)
+                self.list.capacity - 1
             else
                 0;
         }
@@ -115,13 +115,13 @@ pub fn ArrayListSentineled(comptime T: type, comptime sentinel: T) type {
         pub fn appendSlice(self: *Self, m: []const T) !void {
             const old_len = self.len();
             try self.resize(old_len + m.len);
-            mem.copy(T, self.list.span()[old_len..], m);
+            mem.copy(T, self.list.items[old_len..], m);
         }
 
         pub fn append(self: *Self, byte: T) !void {
             const old_len = self.len();
             try self.resize(old_len + 1);
-            self.list.span()[old_len] = byte;
+            self.list.items[old_len] = byte;
         }
 
         pub fn eql(self: Self, m: []const T) bool {
diff --git a/lib/std/build.zig b/lib/std/build.zig
index ccd0ebaf8a..f62448ea1c 100644
--- a/lib/std/build.zig
+++ b/lib/std/build.zig
@@ -1779,7 +1779,7 @@ pub const LibExeObjStep = struct {
         const self = @fieldParentPtr(LibExeObjStep, "step", step);
         const builder = self.builder;
 
-        if (self.root_src == null and self.link_objects.len == 0) {
+        if (self.root_src == null and self.link_objects.items.len == 0) {
             warn("{}: linker needs 1 or more objects to link\n", .{self.step.name});
             return error.NeedAnObject;
         }
@@ -1847,7 +1847,7 @@ pub const LibExeObjStep = struct {
             }
         }
 
-        if (self.build_options_contents.len > 0) {
+        if (self.build_options_contents.items.len > 0) {
             const build_options_file = try fs.path.join(
                 builder.allocator,
                 &[_][]const u8{ builder.cache_root, builder.fmt("{}_build_options.zig", .{self.name}) },
diff --git a/lib/std/build/emit_raw.zig b/lib/std/build/emit_raw.zig
index 367da2f747..f3549491d6 100644
--- a/lib/std/build/emit_raw.zig
+++ b/lib/std/build/emit_raw.zig
@@ -94,7 +94,7 @@ const BinaryElfOutput = struct {
 
         sort.sort(*BinaryElfSegment, self.segments.span(), segmentSortCompare);
 
-        if (self.segments.len > 0) {
+        if (self.segments.items.len > 0) {
             const firstSegment = self.segments.at(0);
             if (firstSegment.firstSection) |firstSection| {
                 const diff = firstSection.elfOffset - firstSegment.elfOffset;
diff --git a/lib/std/coff.zig b/lib/std/coff.zig
index d89019eec6..1ab88f6baf 100644
--- a/lib/std/coff.zig
+++ b/lib/std/coff.zig
@@ -181,7 +181,7 @@ pub const Coff = struct {
     }
 
     pub fn loadSections(self: *Coff) !void {
-        if (self.sections.len == self.coff_header.number_of_sections)
+        if (self.sections.items.len == self.coff_header.number_of_sections)
             return;
 
         try self.sections.ensureCapacity(self.coff_header.number_of_sections);
diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 9e14d132a8..ed327fc6de 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -1478,7 +1478,7 @@ pub const ModuleDebugInfo = switch (builtin.os.tag) {
 
             var coff_section: *coff.Section = undefined;
             const mod_index = for (self.sect_contribs) |sect_contrib| {
-                if (sect_contrib.Section > self.coff.sections.len) continue;
+                if (sect_contrib.Section > self.coff.sections.items.len) continue;
                 // Remember that SectionContribEntry.Section is 1-based.
                 coff_section = &self.coff.sections.span()[sect_contrib.Section - 1];
 
diff --git a/lib/std/dwarf.zig b/lib/std/dwarf.zig
index 95403bc109..3381321330 100644
--- a/lib/std/dwarf.zig
+++ b/lib/std/dwarf.zig
@@ -206,7 +206,7 @@ const LineNumberProgram = struct {
         if (self.target_address >= self.prev_address and self.target_address < self.address) {
             const file_entry = if (self.prev_file == 0) {
                 return error.MissingDebugInfo;
-            } else if (self.prev_file - 1 >= self.file_entries.len) {
+            } else if (self.prev_file - 1 >= self.file_entries.items.len) {
                 return error.InvalidDebugInfo;
             } else
                 &self.file_entries.items[self.prev_file - 1];
@@ -645,7 +645,7 @@ pub const DwarfInfo = struct {
             .offset = abbrev_offset,
             .table = try di.parseAbbrevTable(abbrev_offset),
         });
-        return &di.abbrev_table_list.items[di.abbrev_table_list.len - 1].table;
+        return &di.abbrev_table_list.items[di.abbrev_table_list.items.len - 1].table;
     }
 
     fn parseAbbrevTable(di: *DwarfInfo, offset: u64) !AbbrevTable {
@@ -665,7 +665,7 @@ pub const DwarfInfo = struct {
                 .has_children = (try in.readByte()) == CHILDREN_yes,
                 .attrs = ArrayList(AbbrevAttr).init(di.allocator()),
             });
-            const attrs = &result.items[result.len - 1].attrs;
+            const attrs = &result.items[result.items.len - 1].attrs;
 
             while (true) {
                 const attr_id = try leb.readULEB128(u64, in);
@@ -689,7 +689,7 @@ pub const DwarfInfo = struct {
             .has_children = table_entry.has_children,
             .attrs = ArrayList(Die.Attr).init(di.allocator()),
         };
-        try result.attrs.resize(table_entry.attrs.len);
+        try result.attrs.resize(table_entry.attrs.items.len);
         for (table_entry.attrs.span()) |attr, i| {
             result.attrs.items[i] = Die.Attr{
                 .id = attr.attr_id,
diff --git a/lib/std/fs.zig b/lib/std/fs.zig
index 0eeb1758f2..feb74be2c8 100644
--- a/lib/std/fs.zig
+++ b/lib/std/fs.zig
@@ -1440,9 +1440,9 @@ pub const Walker = struct {
     /// a reference to the path.
     pub fn next(self: *Walker) !?Entry {
         while (true) {
-            if (self.stack.len == 0) return null;
+            if (self.stack.items.len == 0) return null;
             // `top` becomes invalid after appending to `self.stack`.
-            const top = &self.stack.span()[self.stack.len - 1];
+            const top = &self.stack.span()[self.stack.items.len - 1];
             const dirname_len = top.dirname_len;
             if (try top.dir_it.next()) |base| {
                 self.name_buffer.shrink(dirname_len);
@@ -1457,7 +1457,7 @@ pub const Walker = struct {
                         errdefer new_dir.close();
                         try self.stack.append(StackItem{
                             .dir_it = new_dir.iterate(),
-                            .dirname_len = self.name_buffer.len,
+                            .dirname_len = self.name_buffer.items.len,
                         });
                     }
                 }
diff --git a/lib/std/http/headers.zig b/lib/std/http/headers.zig
index a455843539..bcbd6a1e19 100644
--- a/lib/std/http/headers.zig
+++ b/lib/std/http/headers.zig
@@ -139,7 +139,7 @@ pub const Headers = struct {
     pub fn clone(self: Self, allocator: *Allocator) !Self {
         var other = Headers.init(allocator);
         errdefer other.deinit();
-        try other.data.ensureCapacity(self.data.len);
+        try other.data.ensureCapacity(self.data.items.len);
         try other.index.initCapacity(self.index.entries.len);
         for (self.data.span()) |entry| {
             try other.append(entry.name, entry.value, entry.never_index);
@@ -152,7 +152,7 @@ pub const Headers = struct {
     }
 
     pub fn append(self: *Self, name: []const u8, value: []const u8, never_index: ?bool) !void {
-        const n = self.data.len + 1;
+        const n = self.data.items.len + 1;
         try self.data.ensureCapacity(n);
         var entry: HeaderEntry = undefined;
         if (self.index.get(name)) |kv| {
@@ -197,7 +197,7 @@ pub const Headers = struct {
         if (self.index.remove(name)) |kv| {
             var dex = &kv.value;
             // iterate backwards
-            var i = dex.len;
+            var i = dex.items.len;
             while (i > 0) {
                 i -= 1;
                 const data_index = dex.at(i);
@@ -220,18 +220,18 @@ pub const Headers = struct {
         const removed = self.data.orderedRemove(i);
         const kv = self.index.get(removed.name).?;
         var dex = &kv.value;
-        if (dex.len == 1) {
+        if (dex.items.len == 1) {
             // was last item; delete the index
             _ = self.index.remove(kv.key);
             dex.deinit();
             removed.deinit();
             self.allocator.free(kv.key);
         } else {
-            dex.shrink(dex.len - 1);
+            dex.shrink(dex.items.len - 1);
             removed.deinit();
         }
         // if it was the last item; no need to rebuild index
-        if (i != self.data.len) {
+        if (i != self.data.items.len) {
             self.rebuild_index();
         }
     }
@@ -242,18 +242,18 @@ pub const Headers = struct {
         const removed = self.data.swapRemove(i);
         const kv = self.index.get(removed.name).?;
         var dex = &kv.value;
-        if (dex.len == 1) {
+        if (dex.items.len == 1) {
             // was last item; delete the index
             _ = self.index.remove(kv.key);
             dex.deinit();
             removed.deinit();
             self.allocator.free(kv.key);
         } else {
-            dex.shrink(dex.len - 1);
+            dex.shrink(dex.items.len - 1);
             removed.deinit();
         }
         // if it was the last item; no need to rebuild index
-        if (i != self.data.len) {
+        if (i != self.data.items.len) {
             self.rebuild_index();
         }
     }
@@ -277,7 +277,7 @@ pub const Headers = struct {
     pub fn get(self: Self, allocator: *Allocator, name: []const u8) !?[]const HeaderEntry {
         const dex = self.getIndices(name) orelse return null;
 
-        const buf = try allocator.alloc(HeaderEntry, dex.len);
+        const buf = try allocator.alloc(HeaderEntry, dex.items.len);
         var n: usize = 0;
         for (dex.span()) |idx| {
             buf[n] = self.data.at(idx);
@@ -301,7 +301,7 @@ pub const Headers = struct {
 
         // adapted from mem.join
         const total_len = blk: {
-            var sum: usize = dex.len - 1; // space for separator(s)
+            var sum: usize = dex.items.len - 1; // space for separator(s)
             for (dex.span()) |idx|
                 sum += self.data.at(idx).value.len;
             break :blk sum;
@@ -330,7 +330,7 @@ pub const Headers = struct {
             var it = self.index.iterator();
             while (it.next()) |kv| {
                 var dex = &kv.value;
-                dex.len = 0; // keeps capacity available
+                dex.items.len = 0; // keeps capacity available
             }
         }
         { // fill up indexes again; we know capacity is fine from before
diff --git a/lib/std/io/in_stream.zig b/lib/std/io/in_stream.zig
index 340995198f..2a03ba3037 100644
--- a/lib/std/io/in_stream.zig
+++ b/lib/std/io/in_stream.zig
@@ -54,7 +54,7 @@ pub fn InStream(
         /// and the `std.ArrayList` has exactly `max_append_size` bytes appended.
         pub fn readAllArrayList(self: Self, array_list: *std.ArrayList(u8), max_append_size: usize) !void {
             try array_list.ensureCapacity(math.min(max_append_size, 4096));
-            const original_len = array_list.len;
+            const original_len = array_list.items.len;
             var start_index: usize = original_len;
             while (true) {
                 array_list.expandToCapacity();
@@ -106,7 +106,7 @@ pub fn InStream(
                     return;
                 }
 
-                if (array_list.len == max_size) {
+                if (array_list.items.len == max_size) {
                     return error.StreamTooLong;
                 }
 
diff --git a/lib/std/json.zig b/lib/std/json.zig
index 12020e6e25..79830d8a2c 100644
--- a/lib/std/json.zig
+++ b/lib/std/json.zig
@@ -1556,7 +1556,7 @@ fn parseInternal(comptime T: type, token: Token, tokens: *TokenStream, options:
                                     else => {},
                                 }
 
-                                try arraylist.ensureCapacity(arraylist.len + 1);
+                                try arraylist.ensureCapacity(arraylist.items.len + 1);
                                 const v = try parseInternal(ptrInfo.child, tok, tokens, options);
                                 arraylist.appendAssumeCapacity(v);
                             }
@@ -1874,7 +1874,7 @@ pub const Parser = struct {
             try p.transition(&arena.allocator, input, s.i - 1, token);
         }
 
-        debug.assert(p.stack.len == 1);
+        debug.assert(p.stack.items.len == 1);
 
         return ValueTree{
             .arena = arena,
@@ -1888,7 +1888,7 @@ pub const Parser = struct {
         switch (p.state) {
             .ObjectKey => switch (token) {
                 .ObjectEnd => {
-                    if (p.stack.len == 1) {
+                    if (p.stack.items.len == 1) {
                         return;
                     }
 
@@ -1907,8 +1907,8 @@ pub const Parser = struct {
                 },
             },
             .ObjectValue => {
-                var object = &p.stack.items[p.stack.len - 2].Object;
-                var key = p.stack.items[p.stack.len - 1].String;
+                var object = &p.stack.items[p.stack.items.len - 2].Object;
+                var key = p.stack.items[p.stack.items.len - 1].String;
 
                 switch (token) {
                     .ObjectBegin => {
@@ -1950,11 +1950,11 @@ pub const Parser = struct {
                 }
             },
             .ArrayValue => {
-                var array = &p.stack.items[p.stack.len - 1].Array;
+                var array = &p.stack.items[p.stack.items.len - 1].Array;
 
                 switch (token) {
                     .ArrayEnd => {
-                        if (p.stack.len == 1) {
+                        if (p.stack.items.len == 1) {
                             return;
                         }
 
@@ -2021,12 +2021,12 @@ pub const Parser = struct {
     }
 
     fn pushToParent(p: *Parser, value: *const Value) !void {
-        switch (p.stack.span()[p.stack.len - 1]) {
+        switch (p.stack.span()[p.stack.items.len - 1]) {
             // Object Parent -> [ ..., object, <key>, value ]
             Value.String => |key| {
                 _ = p.stack.pop();
 
-                var object = &p.stack.items[p.stack.len - 1].Object;
+                var object = &p.stack.items[p.stack.items.len - 1].Object;
                 _ = try object.put(key, value.*);
                 p.state = .ObjectKey;
             },
@@ -2165,7 +2165,7 @@ test "json.parser.dynamic" {
     testing.expect(animated.Bool == false);
 
     const array_of_object = image.Object.get("ArrayOfObject").?.value;
-    testing.expect(array_of_object.Array.len == 1);
+    testing.expect(array_of_object.Array.items.len == 1);
 
     const obj0 = array_of_object.Array.at(0).Object.get("n").?.value;
     testing.expect(mem.eql(u8, obj0.String, "m"));
diff --git a/lib/std/math/big/rational.zig b/lib/std/math/big/rational.zig
index cf88558576..8d2932a920 100644
--- a/lib/std/math/big/rational.zig
+++ b/lib/std/math/big/rational.zig
@@ -4,7 +4,6 @@ const math = std.math;
 const mem = std.mem;
 const testing = std.testing;
 const Allocator = mem.Allocator;
-const ArrayList = std.ArrayList;
 
 const bn = @import("int.zig");
 const Limb = bn.Limb;
diff --git a/lib/std/net.zig b/lib/std/net.zig
index 0f7118c331..f91b2b86aa 100644
--- a/lib/std/net.zig
+++ b/lib/std/net.zig
@@ -509,7 +509,7 @@ pub fn getAddressList(allocator: *mem.Allocator, name: []const u8, port: u16) !*
 
         try linuxLookupName(&lookup_addrs, &canon, name, family, flags, port);
 
-        result.addrs = try arena.alloc(Address, lookup_addrs.len);
+        result.addrs = try arena.alloc(Address, lookup_addrs.items.len);
         if (!canon.isNull()) {
             result.canon_name = canon.toOwnedSlice();
         }
@@ -554,7 +554,7 @@ fn linuxLookupName(
             return name_err;
         } else {
             try linuxLookupNameFromHosts(addrs, canon, name, family, port);
-            if (addrs.len == 0) {
+            if (addrs.items.len == 0) {
                 try linuxLookupNameFromDnsSearch(addrs, canon, name, family, port);
             }
         }
@@ -562,11 +562,11 @@ fn linuxLookupName(
         try canon.resize(0);
         try linuxLookupNameFromNull(addrs, family, flags, port);
     }
-    if (addrs.len == 0) return error.UnknownHostName;
+    if (addrs.items.len == 0) return error.UnknownHostName;
 
     // No further processing is needed if there are fewer than 2
     // results or if there are only IPv4 results.
-    if (addrs.len == 1 or family == os.AF_INET) return;
+    if (addrs.items.len == 1 or family == os.AF_INET) return;
     const all_ip4 = for (addrs.span()) |addr| {
         if (addr.addr.any.family != os.AF_INET) break false;
     } else true;
@@ -908,7 +908,7 @@ fn linuxLookupNameFromDnsSearch(
         canon.shrink(canon_name.len + 1);
         try canon.appendSlice(tok);
         try linuxLookupNameFromDns(addrs, canon, canon.span(), family, rc, port);
-        if (addrs.len != 0) return;
+        if (addrs.items.len != 0) return;
     }
 
     canon.shrink(canon_name.len);
@@ -967,7 +967,7 @@ fn linuxLookupNameFromDns(
         dnsParse(ap[i], ctx, dnsParseCallback) catch {};
     }
 
-    if (addrs.len != 0) return;
+    if (addrs.items.len != 0) return;
     if (ap[0].len < 4 or (ap[0][3] & 15) == 2) return error.TemporaryNameServerFailure;
     if ((ap[0][3] & 15) == 0) return error.UnknownHostName;
     if ((ap[0][3] & 15) == 3) return;
@@ -1049,7 +1049,7 @@ fn getResolvConf(allocator: *mem.Allocator, rc: *ResolvConf) !void {
         }
     }
 
-    if (rc.ns.len == 0) {
+    if (rc.ns.items.len == 0) {
         return linuxLookupNameFromNumericUnspec(&rc.ns, "127.0.0.1", 53);
     }
 }
@@ -1078,7 +1078,7 @@ fn resMSendRc(
     var ns_list = std.ArrayList(Address).init(rc.ns.allocator);
     defer ns_list.deinit();
 
-    try ns_list.resize(rc.ns.len);
+    try ns_list.resize(rc.ns.items.len);
     const ns = ns_list.span();
 
     for (rc.ns.span()) |iplit, i| {
diff --git a/lib/std/special/build_runner.zig b/lib/std/special/build_runner.zig
index 665d47c1bd..1c88f98e6e 100644
--- a/lib/std/special/build_runner.zig
+++ b/lib/std/special/build_runner.zig
@@ -171,7 +171,7 @@ fn usage(builder: *Builder, already_ran_build: bool, out_stream: var) !void {
         \\
     );
 
-    if (builder.available_options_list.len == 0) {
+    if (builder.available_options_list.items.len == 0) {
         try out_stream.print("  (none)\n", .{});
     } else {
         for (builder.available_options_list.span()) |option| {
diff --git a/lib/std/unicode.zig b/lib/std/unicode.zig
index a971a730e8..333287b351 100644
--- a/lib/std/unicode.zig
+++ b/lib/std/unicode.zig
@@ -475,7 +475,7 @@ pub fn utf16leToUtf8Alloc(allocator: *mem.Allocator, utf16le: []const u16) ![]u8
     var it = Utf16LeIterator.init(utf16le);
     while (try it.nextCodepoint()) |codepoint| {
         const utf8_len = utf8CodepointSequenceLength(codepoint) catch unreachable;
-        try result.resize(result.len + utf8_len);
+        try result.resize(result.items.len + utf8_len);
         assert((utf8Encode(codepoint, result.items[out_index..]) catch unreachable) == utf8_len);
         out_index += utf8_len;
     }
@@ -571,7 +571,7 @@ pub fn utf8ToUtf16LeWithNull(allocator: *mem.Allocator, utf8: []const u8) ![:0]u
         }
     }
 
-    const len = result.len;
+    const len = result.items.len;
     try result.append(0);
     return result.toOwnedSlice()[0..len :0];
 }
diff --git a/src-self-hosted/libc_installation.zig b/src-self-hosted/libc_installation.zig
index 60124d30e5..f3441cec0d 100644
--- a/src-self-hosted/libc_installation.zig
+++ b/src-self-hosted/libc_installation.zig
@@ -268,7 +268,7 @@ pub const LibCInstallation = struct {
                 try search_paths.append(line);
             }
         }
-        if (search_paths.len == 0) {
+        if (search_paths.items.len == 0) {
             return error.CCompilerCannotFindHeaders;
         }
 
@@ -276,9 +276,9 @@ pub const LibCInstallation = struct {
         const sys_include_dir_example_file = if (is_windows) "sys\\types.h" else "sys/errno.h";
 
         var path_i: usize = 0;
-        while (path_i < search_paths.len) : (path_i += 1) {
+        while (path_i < search_paths.items.len) : (path_i += 1) {
             // search in reverse order
-            const search_path_untrimmed = search_paths.at(search_paths.len - path_i - 1);
+            const search_path_untrimmed = search_paths.at(search_paths.items.len - path_i - 1);
             const search_path = std.mem.trimLeft(u8, search_path_untrimmed, " ");
             var search_dir = fs.cwd().openDir(search_path, .{}) catch |err| switch (err) {
                 error.FileNotFound,
diff --git a/src-self-hosted/stage2.zig b/src-self-hosted/stage2.zig
index 43e0a8ffca..b63b6e8ca8 100644
--- a/src-self-hosted/stage2.zig
+++ b/src-self-hosted/stage2.zig
@@ -239,7 +239,7 @@ fn fmtMain(argc: c_int, argv: [*]const [*:0]const u8) !void {
     }
 
     if (stdin_flag) {
-        if (input_files.len != 0) {
+        if (input_files.items.len != 0) {
             try stderr.writeAll("cannot use --stdin with positional arguments\n");
             process.exit(1);
         }
@@ -273,7 +273,7 @@ fn fmtMain(argc: c_int, argv: [*]const [*:0]const u8) !void {
         return;
     }
 
-    if (input_files.len == 0) {
+    if (input_files.items.len == 0) {
         try stderr.writeAll("expected at least one source file argument\n");
         process.exit(1);
     }
diff --git a/src-self-hosted/translate_c.zig b/src-self-hosted/translate_c.zig
index 6ba7fc8ca1..a7622a3ffa 100644
--- a/src-self-hosted/translate_c.zig
+++ b/src-self-hosted/translate_c.zig
@@ -4309,7 +4309,7 @@ fn makeRestorePoint(c: *Context) RestorePoint {
     return RestorePoint{
         .c = c,
         .token_index = c.tree.tokens.len,
-        .src_buf_index = c.source_buffer.len,
+        .src_buf_index = c.source_buffer.items.len,
     };
 }
 
@@ -4771,11 +4771,11 @@ fn appendToken(c: *Context, token_id: Token.Id, bytes: []const u8) !ast.TokenInd
 
 fn appendTokenFmt(c: *Context, token_id: Token.Id, comptime format: []const u8, args: var) !ast.TokenIndex {
     assert(token_id != .Invalid);
-    const start_index = c.source_buffer.len;
+    const start_index = c.source_buffer.items.len;
     errdefer c.source_buffer.shrink(start_index);
 
     try c.source_buffer.outStream().print(format, args);
-    const end_index = c.source_buffer.len;
+    const end_index = c.source_buffer.items.len;
     const token_index = c.tree.tokens.len;
     const new_token = try c.tree.tokens.addOne();
     errdefer c.tree.tokens.shrink(token_index);
diff --git a/test/standalone/brace_expansion/main.zig b/test/standalone/brace_expansion/main.zig
index 411f2bfaf6..8abe39a428 100644
--- a/test/standalone/brace_expansion/main.zig
+++ b/test/standalone/brace_expansion/main.zig
@@ -113,7 +113,7 @@ fn parse(tokens: *const ArrayList(Token), token_index: *usize) ParseError!Node {
 
 fn expandString(input: []const u8, output: *ArrayListSentineled(u8, 0)) !void {
     const tokens = try tokenize(input);
-    if (tokens.len == 1) {
+    if (tokens.items.len == 1) {
         return output.resize(0);
     }
 
@@ -142,7 +142,7 @@ fn expandString(input: []const u8, output: *ArrayListSentineled(u8, 0)) !void {
 const ExpandNodeError = error{OutOfMemory};
 
 fn expandNode(node: Node, output: *ArrayList(ArrayListSentineled(u8, 0))) ExpandNodeError!void {
-    assert(output.len == 0);
+    assert(output.items.len == 0);
     switch (node) {
         Node.Scalar => |scalar| {
             try output.append(try ArrayListSentineled(u8, 0).init(global_allocator, scalar));
diff --git a/test/tests.zig b/test/tests.zig
index 8ad5803184..e66ae7296a 100644
--- a/test/tests.zig
+++ b/test/tests.zig
@@ -879,13 +879,13 @@ pub const CompileErrorContext = struct {
                 var err_iter = ErrLineIter.init(stderr);
                 var i: usize = 0;
                 ok = while (err_iter.next()) |line| : (i += 1) {
-                    if (i >= self.case.expected_errors.len) break false;
+                    if (i >= self.case.expected_errors.items.len) break false;
                     const expected = self.case.expected_errors.at(i);
                     if (mem.indexOf(u8, line, expected) == null) break false;
                     continue;
                 } else true;
 
-                ok = ok and i == self.case.expected_errors.len;
+                ok = ok and i == self.case.expected_errors.items.len;
 
                 if (!ok) {
                     warn("\n======== Expected these compile errors: ========\n", .{});
diff --git a/tools/merge_anal_dumps.zig b/tools/merge_anal_dumps.zig
index 10c401ec38..3cd23f6246 100644
--- a/tools/merge_anal_dumps.zig
+++ b/tools/merge_anal_dumps.zig
@@ -194,7 +194,7 @@ const Dump = struct {
         for (other_files) |other_file, i| {
             const gop = try self.file_map.getOrPut(other_file.String);
             if (!gop.found_existing) {
-                gop.kv.value = self.file_list.len;
+                gop.kv.value = self.file_list.items.len;
                 try self.file_list.append(other_file.String);
             }
             try other_file_to_mine.putNoClobber(i, gop.kv.value);
@@ -213,7 +213,7 @@ const Dump = struct {
             };
             const gop = try self.node_map.getOrPut(other_node);
             if (!gop.found_existing) {
-                gop.kv.value = self.node_list.len;
+                gop.kv.value = self.node_list.items.len;
                 try self.node_list.append(other_node);
             }
             try other_ast_node_to_mine.putNoClobber(i, gop.kv.value);
@@ -243,7 +243,7 @@ const Dump = struct {
             };
             const gop = try self.error_map.getOrPut(other_error);
             if (!gop.found_existing) {
-                gop.kv.value = self.error_list.len;
+                gop.kv.value = self.error_list.items.len;
                 try self.error_list.append(other_error);
             }
             try other_error_to_mine.putNoClobber(i, gop.kv.value);
@@ -304,7 +304,7 @@ const Dump = struct {
     ) !void {
         const gop = try self.type_map.getOrPut(other_type);
         if (!gop.found_existing) {
-            gop.kv.value = self.type_list.len;
+            gop.kv.value = self.type_list.items.len;
             try self.type_list.append(other_type);
         }
         try other_types_to_mine.putNoClobber(other_type_index, gop.kv.value);